Currently, receiving terminal devices adopting the On-Off Keying (OOK) modulation system may use two types of demodulation circuit topologies. The first type of OOK demodulation circuit topology may be, for example, a Direct Radio Frequency (DRF) demodulation circuit. The DRF demodulation circuit amplifies a received radio frequency (RF) signal through a first stage amplifier (i.e., a linear amplifier) circuit, and then performs an envelop detection on the received RF signal (which had been amplified by the first stage amplifier circuit) through a second stage amplifier (i.e., a nonlinear amplifier) to obtain the data in the received RF signal. The OOK demodulation circuit topology may encounter a situation that when power consumption of the overall receiver needs to be lowered, the gain of the first stage amplifier circuit is simultaneously lowered, which results in an overall system sensitivity being lowered.
The second type of the OOK demodulation circuit topology may be, for example, an Uncertain Intermediate Frequency (UIF) demodulation circuit. The UIF demodulation circuit separates the first stage amplifier (i.e., a linear amplifier) circuit of the previous DRF demodulation circuit into two amplification stages. A first amplification stage performs a high-frequency amplification on the received RF signal, and down-converts the amplified RF signal into an intermediate frequency (IF) signal (whose frequency is lower than the RF signal). The second amplification stage performs an intermediate frequency amplification on the IF signal, and then allocates a larger portion of gain of the UIF demodulation circuit to the second amplification stage to avoid the trade-off between the high frequency gain and the power consumption. However, under a requirement of lowering the power consumption of the overall receiver for the UIF demodulation circuit with the conventional UIF demodulator topology, the gain of the high-frequency amplification circuit is simultaneously lowered and this results in a lower noise figure and finally lowers the overall system sensitivity.
Therefore, there are main issues for the industry to research how to enhance receiving sensitivity of the overall receiver system without additional power consumption for the receiver of the communication system adopting the OOK modulation, or how to maintain the same system sensitivity with a lower overall power consumption.